My trusty old Butternut vertical gets a new lease of life

It's been sitting at the end of the garden for years, stored behind the shed. My trusty (and admittedly dirty) old Butternut HF6V vertical antenna is back in the air. I re-erected it last week, but found signals on the bands quite attenuated compared with my nested inverted vees.

What followed was a patient game of "adjust, test, adjust, test, adjust more, test more..." as I tried to bring the antenna into resonance on the six bands where it is designed to operate.

Given that the SWR was high (at least 5:1 on most bands), a quick read of the 28-page manual for the antenna (yes, I RTFM'd!) revealed that when SWR is reading high across the bands, this is likely to be because of a problem with the feeder.

The Butternut is fed with a quarter-wave section of 75 ohm coax which is used as a "geometric mean transformer" to match the approximate 100 ohms of feedpoint impedance on the 20 metre band to a 50 ohm main transmission line.

I suspected that there was an issue with the 75 ohm coax, and particularly where it connects with the Butternut. Yesterday, I disconnected the coax from the Butternut and fed it into the shack, where I was able to cut a couple of centimetres off and begin to reveal the core and braid so that I could re-attach the coax to the antenna.

The coax is difficult to work with because it's very stiff, and the core is solid. I soldered a short length (approx 10cm) of insulated electrical earth wire to the braid and taped it up using insulating tape. I also cleaned the connecting screws on the antenna and replaced the washers with new ones.

When I re-attached the coax, the antenna was sounding "louder" (less attenuated than before), but quick tests at the radio and with an analyser revealed the SWR was still high across the board.

What followed today was an exercise in patience and meticulous adjustments. The Butternut HF6V has three L/C assemblies - one for 80 metres, one for 40m and one for 30m. Upon making adjustments to the 80m coil, I was able to get resonance on that band. In fact, I was really thrilled to get the SWR all the way down to 1.0:1 at the bottom end of 80 - just above 3.5Mhz, where I love trying to work DX on CW.

By old Butternut HF6V is back in the air.

A great start, but some time and patience was needed for 40m, where lots of adjustments of the coil were needed to eventually get the SWR to a respectable 1.2:1 at the top of the band and 1.9:1 on the CW portion. I can certainly live with that! The Butternut will give me an advantage on the low bands because it offers a lower angle of radiation than the inverted vees, which in truth are not high enough at the apex, being just 10 metres at the feed point.

The 30 metre band proved extremely finicky. Very small adjustments of the 30m coil on the Butternut HF6V can shift the lowest SWR frequency by 100Khz! After making something like a dozen or fifteen changes, I eventually settled for an SWR of about 2.2:1 on 10Mhz - realising that that was much better than the 5:1 I had been seeing after just very minor movements of the coil.

For now, the SWR on 20 metres is high. It is reading a 5:1 or slightly higher across the entire band. Not ideal obviously. I did try to change the position of the coil support tube 30 meter L bracket where it attaches to the 40 metre coil, as instructed by the manual, but was unable to see a lower SWR. I will have to think about my strategy for 20m resonance. Should I replace the 75 ohm transformer coax? Or tinker with the 30m L bracket some more? I am afraid to do too much because I have a good SWR on 80m and 40m, where I really want it.

On 15 metres, with no further adjustments the antenna presented an SWR of 2:1 at 21.005Mhz and 1.5:1 at 21.345Mhz, which is nice. The Butternut HF6V does not resonate on 17 metres. On 12 metres, it has an SWR of 1.4:1 across the band, while on 10 metres it had "acceptable" SWR values varying only very slightly from 28.000Mhz to 28.500Mhz from 2.2:1 to 2.3:1.

In all honesty though, if you quickly glanced at my Butternut, you would wonder how the thing radiates at all. It came into my possession just after I got licenced in the winter of 2009. My very good friend and mentor, Tony EI4DIB (now sadly silent key), had acquired it - I think from a ham in GI/Northern Ireland - and had it stored in his back garden. I reckon it had spent a number of years in what might be termed "outdoor storage". It was filthy, covered with grime and dirt, and had long ago lost its sheen.

However, when Tony and I installed it at my QTH back in 2009, it did work. It radiated. I'm not sure how effectively, but I was able to make QSOs. In January 2010, using just 100 watts, I made my first ever QSO with Australia using the Butternut, although admittedly I had to wait until the pile-up dissipated and there was nobody else calling before I could be heard. That station was VI2AJ2010, a special event station for the 22nd Australian Scouts 2010 Jamboree in Appin, New South Wales.

The Butternut was my main HF antenna for a while, before I acquired an MA5B minibeam, and later a hexbeam. I cannot remember when I took it down, but it might be as long as 10 years ago or more. I wondered if it would ever see use again. Thankfully, it is radiating RF as I write this, on 15 metres FT8, and is actually showing an SWR of 1.4:1 on 21.074Mhz.

Last week, when I re-erected it, I noticed that an aluminium strip which was part of the 40 metre L/C circuit was missing. Thankfully, I have some Butternut HF6V "spare parts" (which again I have Tony to thank for, because he spotted them in a box at a radio rally and I got them for next to nothing), and was able to solder a new nut on to the 40m capacitor, drill a hole into a spare aluminium strip and bolt it on.

That was certainly a bit of what might be termed "homebrewing" or improvisation, but it works.

I look forward to testing the Butternut as soon as possible on 80 metres. That band has been very fruitful this summer, giving me four or five new DXCC in recent weeks, mostly on FT8. When I was studying for my ham licence, and even for several years after getting licenced, it was commonly held that 80 metres should be avoided during the summer because it's a nighttime band and the DX was only there in the winter. However, at this latitude (53 degrees north), in midsummer we have an extended grey line, which offers lots of opportunity for DX contacts. 

Some of those new DXCCs on 80 were Angola, Paraguay and Singapore, and on one evening in the past week I worked THREE stations in Western Australia on 3.573Mhz using FT8. It will be interesting to see, using a combination of CW and FT8, and watching the Reverse Beacon Network and PSK Reporter, how the Butternut performs compared with the dipoles.